Method for achieving smooth side walls after Bosch etch process

Abstract

A method is provided for etching silicon in a plasma processing chamber, having an operating pressure and an operating bias. The method includes: performing a first vertical etch in the silicon to create a hole having a first depth and a sidewall; performing a deposition of a protective layer on the sidewall; performing a second vertical etch to deepen the hole to a second depth and to create a second sidewall, the second sidewall including a first trough, a second trough and a peak, the first trough corresponding to the first sidewall, the second trough corresponding to the second sidewall, the peak being disposed between the first trough and the second trough; and performing a third etch to reduce the peak.

What is claimed as new and desired to be protected by Letters Patent of the United States is: 
     
       1. A method of etching silicon in a plasma processing chamber, said method comprising:
 operating the plasma processing chamber at a first pressure and a first bias to perform a first vertical etch in the silicon to create a hole having a first depth and a sidewall; 
 operating the plasma processing chamber at a second pressure and a second bias to perform a deposition of a protective layer on the sidewall; 
 operating the plasma processing chamber at a third pressure and a third bias to perform a second vertical etch to deepen the hole to a second depth and to create a second sidewall, the second sidewall including a first trough, a second trough and a peak, the first trough corresponding to the first sidewall, the second trough corresponding to the second sidewall, the peak being disposed between the first trough and the second trough; and 
 operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak, 
 wherein the fourth bias is sufficient to induce ion bombardment to eliminate the peak. 
 
     
     
       2. The method of  claim 1 , wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber with an operating pressure in the range of 15 to 100 mtorr. 
     
     
       3. The method of  claim 2 , wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber at an operating bias in the range of 200 to 1000 V. 
     
     
       4. The method of  claim 3 , wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber at the fourth pressure and the fourth bias to perform the third etch for 30-180 seconds. 
     
     
       5. The method of  claim 4 , wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber at the fourth pressure and the fourth bias to perform the third etch with one of NF3, CF4, SF6, and combinations thereof. 
     
     
       6. The method of  claim 3 , wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber at the fourth pressure and the fourth bias to perform the third etch with one of NF3, CF4, SF6, and combinations thereof. 
     
     
       7. The method of  claim 2 , wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber at the fourth pressure and the fourth bias to perform the third etch for 30-180 seconds. 
     
     
       8. The method of  claim 7 , wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber at the fourth pressure and the fourth bias to perform the third etch with one of NF3, CF4, SF6, and combinations thereof. 
     
     
       9. The method of  claim 2 , wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber at the fourth pressure and the fourth bias to perform the third etch with one of NF3, CF4, SF6, and combinations thereof. 
     
     
       10. The method of  claim 1 , wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber at an operating bias in the range of 200 to 1000 V. 
     
     
       11. The method of  claim 10 , wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber at the fourth pressure and the fourth bias to perform the third etch with one of NF3, CF4, SF6, and combinations thereof. 
     
     
       12. The method of  claim 1 , wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber at the fourth pressure and the fourth bias to perform the third etch for 15-180 seconds, and wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber at the fourth pressure and the fourth bias to perform the third etch with one of NF3, CF4, SF6, and combinations thereof. 
     
     
       13. The method of  claim 1 , wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber at the fourth pressure and the fourth bias to perform the third etch with one of NF3, CF4, SF6, and combinations thereof. 
     
     
       14. A method of etching silicon in a plasma processing chamber, said method comprising:
 operating the plasma processing chamber to perform a first vertical etch in the silicon to create a hole having a first depth and a sidewall; 
 operating the plasma processing chamber to perform a deposition of a protective layer on the sidewall; 
 operating the plasma processing chamber to perform a second vertical etch to deepen the hole to a second depth and to create a second sidewall, the second sidewall including a first trough, a second trough and a peak, the first trough corresponding to the first sidewall, the second trough corresponding to the second sidewall, the peak being disposed between the first trough and the second trough; 
 providing a mixture of CF 4  and at least one of the group consisting of CHF 3 , CH 2 F 2 , C 2 F 6 , C 2 F 4 H 2 , and combinations thereof; and 
 operating the plasma processing chamber to perform a third etch to eliminate the peak. 
 
     
     
       15. The method of  claim 14 , wherein said operating the plasma processing chamber to perform a third etch to eliminate the peak comprises operating the plasma processing chamber with an operating pressure in the range of 15 to 100 mtorr. 
     
     
       16. The method of  claim 14 , wherein operating the plasma processing chamber to perform a third etch to eliminate the peak comprises operating the plasma processing chamber with an operating bias in the processing chamber being in the range of 200 to 1000 V. 
     
     
       17. The method of  claim 14 , wherein said operating the plasma processing chamber to perform a third etch to eliminate the peak comprises operating the plasma processing chamber to perform a third etch for 30-180 seconds. 
     
     
       18. The method of  claim 1 , wherein said operating the plasma processing chamber at a fourth pressure and a fourth bias to perform a third etch to reduce the peak comprises operating the plasma processing chamber with an operating pressure in the range of 40 to 80 mtorr. 
     
     
       19. The method of  claim 1 , wherein said bias directs gas ions to the peaks so as to preferentially remove the peaks while maintaining the diameter of the etched hole.